The invention relates to a control valve for a device for variably adjusting the valve timing for gas-exchange valves in an internal combustion engine and to a use of a non-return valve located in an annular groove for a pressurized medium circuit of a device for variably adjusting the valve timing for gas-exchange valves in an internal combustion engine.
In internal combustion engines, camshafts are used for actuating gas-exchange valves. Camshafts are mounted in the internal combustion engine such that cams mounted on these camshafts contact cam followers, for example, cup tappets, finger levers, or rocker levers. If a camshaft is set in rotation, then the cams roll on the cam followers, which in turn actuate the gas-exchange valves. Thus, both the opening period and also the opening amplitude, but also the opening and closing times of the gas-exchange valves, are set through the position and the shape of the cams.
During the actuation of the gas-exchange valves, the valve springs exert a force on the cams of the camshaft, by which alternating moments act on the camshaft.
Modern motor concepts look toward designing a variable valve train. On one hand, the valve stroke and valve opening period should be variable until the individual cylinder is completely shut down. For this purpose there are concepts, such as switchable cam followers or electro-hydraulic or electric valve actuators. Furthermore, it has been shown to be advantageous to be able to influence the opening and closing times of gas-exchange valves during the operation of the internal combustion engine. Here it is especially advantageous to be able to influence the opening or closing times of the intake or exhaust valves separately, in order to selectively adjust, for example, a defined valve overlap. By adjusting the opening or closing times of the gas-exchange valves as a function of the current characteristic diagram of the motor, for example, the current rotational speed or the current load, the specific fuel consumption can be reduced, the exhaust-gas behavior can be positively influenced, and the engine efficiency, the maximum torque, and the maximum output can be increased.
The described variability of the gas-exchange valve control times is achieved through a relative change of the phase position of the camshaft relative to the crankshaft. Here, the camshaft is usually in driven connection with the crankshaft via a chain, belt, or gear drive, or an identically acting drive concept. Between the chain, belt, or gear drive driven by the crankshaft and the camshaft there is a device for variably adjusting the valve timing of gas-exchange valves in an internal combustion engine, also called a camshaft adjuster below, which transfers the torque from the crankshaft to the camshaft. Here, this device is constructed so that during the operation of the internal combustion engine, the phase position between the crankshaft and the camshaft is maintained and, if desired, the camshaft can be rotated in a certain angular range relative to the crankshaft.
In internal combustion engines with a separate camshaft for the intake and the exhaust valves, each camshaft can be equipped with a camshaft adjuster. Therefore, the opening and closing times of the intake and exhaust gas-exchange valves can be shifted in time relative to each other and the valve overlap can be selectively adjusted.
The location of modern camshaft adjusters is usually on the drive-side end of the camshaft. The camshaft adjuster can also be arranged, however, on an intermediate shaft, a non-rotating component, or the crankshaft. It is composed of a driving wheel, which is driven by the crankshaft and which maintains a fixed phase relationship to the crankshaft, a driven element in driving connection with the camshaft, and an adjustment mechanism transferring the torque from the driving wheel to the driven element. The driving wheel can be constructed in the case of a camshaft adjuster not arranged on the crankshaft as a chain, belt, or gear wheel and is driven by the crankshaft via a chain, belt, or gear drive. The adjustment mechanism can be operated electrically, hydraulically, or pneumatically.
The so-called axial piston adjuster and the rotary piston adjuster represent two preferred embodiments of hydraulically adjustable camshaft adjusters.
For axial piston adjusters, the driving wheel is connected to a piston and this is connected to the driven element each via spiral gearing. The piston separates a hollow space formed by the driven element and the driving wheel into two pressure chambers arranged axial relative to each other. If one pressure chamber is now pressurized with a pressurized medium, while the other pressure chamber is connected to a tank, then the piston is displaced in the axial direction. The axial displacement of the piston is transferred by the spiral gearing into a relative rotation of the driving wheel to the driven element and thus of the camshaft to the crankshaft.
A second embodiment of a hydraulic camshaft adjuster is the so-called rotary piston adjuster. In these adjusters, the driving wheel is locked in rotation with a stator. The stator and the driven element (rotor) are arranged concentric to each other, wherein the rotor is connected with a non-positive fit, positive fit, or material fit, for example, using a press fit, a screw or weld connection, to a camshaft, an extension of the camshaft or an intermediate shaft. In the stator, several recesses spaced apart in the peripheral direction are formed, which extend radially outwardly starting from the rotor. The recesses are limited in the axial direction in a pressure-tight manner by side covers. A vane connected to the rotor extends into each of these recesses, wherein each recess is divided into two pressure chambers. Therefore, two groups of pressure chambers are formed. Through the selective connection of one group of pressure chambers to a pressurized medium pump and the other group of pressure chambers to a tank, the phase of the camshaft can be adjusted or maintained relative to the crankshaft. The vanes can be constructed, for example, in one part with the rotor or as separate components, which are arranged in an axial vane groove on the outer casing surface of the rotor and which are forced radially outward by a spring element.
For controlling the camshaft adjuster, sensors detect the characteristic data of the motor, such as, for example, the current phase position of the camshaft to the crankshaft, the load state, and the rotational speed. This data is fed to an electronic control unit, which controls the feeding and discharge of pressurized medium to the various pressure chambers after comparing the data with a characteristic diagram of the internal combustion engine.
To adjust the phase position of the camshaft relative to the crankshaft, in hydraulic camshaft adjusters one of the two oppositely acting pressure chambers are connected to a pressurized medium pump and the other is connected to the tank. The inflow of pressurized medium to a chamber in connection with the outflow of pressurized medium from the other chamber displaces the piston/vane separating the pressure chambers, wherein the camshaft is turned relative to the crankshaft in axial piston adjusters through an axial displacement of the piston by the spiral gearing. In rotary piston adjusters, through the pressurization of one group of pressure chambers and the relaxation of pressure in the other group of pressure chambers, the vane is displaced in the peripheral direction and thus the camshaft rotates relative to the crankshaft directly. To maintain the phase position, both pressure chambers are connected either to the pressurized medium pump or both are separated from the pressurized medium pump and also from the tank.
The control of the pressurized medium flows to or from the pressure chambers is performed by a control valve, usually a 4/3 proportional valve. This is comprised essentially from a hollow cylindrical valve housing, a control piston, and an adjustment unit. Each valve housing is provided with a connection for each group of identically acting pressure chambers (work connection), a connection to the pressurized medium pump, and at least one connection to a tank. These connections are usually constructed as annular grooves on the outer casing surface of the valve housing, which communicate with the interior of the control piston via radial openings. Within the valve housing, the control piston is arranged so that it can be displaced in the axial direction. The control piston can be positioned by the adjustment unit, which is usually actuated electromagnetically or hydraulically, against the spring force of a spring element in any position in the axial direction between two defined end positions. The outer casing surface of the control piston is essentially adapted to the inner diameter of the valve housing and is provided with annular grooves and control edges. Through control of the adjustment unit, the individual connections can be connected hydraulically to each other, wherein the individual pressure chambers can be connected selectively to the pressurized medium pump or to the tank. Likewise, a position of the control piston can be provided, in which the pressurized medium chambers are separated both from the pressurized medium pump and also from the pressurized medium tank.
Such a control valve is known from JP 07-229408A. In this case, five annular grooves spaced apart from each other are constructed on the outer casing surface of the valve housing, wherein each of the annular grooves is used as a connection of the valve. In each groove base of the annular grooves, a radial opening is formed, which opens into the interior of the valve housing. Here, openings of adjacent groove bases are offset relative to each other in the peripheral direction by 180°.
Within the valve housing there is a solid control piston, which can be positioned by an electromagnetic adjustment unit against the force of a spring within the valve housing in the axial direction between two end stops. The outer diameter of the control piston is adapted to the inner diameter of the valve housing. In addition, three annular grooves are formed on the control piston, by, dependent on the position of the control piston relative to the valve housing, adjacent connections can be connected to each other.
From DE 198 53 670 A1, another embodiment of such a control valve is known. This differs from the embodiment shown in JP 07-229408A in that the control piston has a hollow construction. In addition, on the outer casing surface of the valve housing, only three connections are formed, wherein a fourth connection is constructed in the axial direction of the valve housing. The pressurized medium can now be led to one of the two work connections via the axial inlet connection according to the position of the control piston relative to the valve housing. Simultaneously, the other work connection is connected to the tank connection via an annular groove formed on the outer casing surface of the control piston.
In this embodiment of a control valve, the position of the inlet connection and the tank connection are exchangeable.
By rolling the cam of a camshaft on the cam follower of a valve train, periodically alternating moments act on the camshaft. These alternating moments are transferred to the rotor of the camshaft adjuster, wherein pressure spikes are produced in the pressure chambers. To prevent these pressure spikes from being transferred via pressurized medium lines and the control valve into the pressurized medium circuit of the internal combustion engine, non-return valves are provided between the control valve and the pressurized medium pump. Here, non-return valves that are separate or that are integrated into the control valve can be provided. A non-return valve integrated in the control valve is shown, for example, in EP 1 291 563 A2. In this embodiment, a closing element made from a band bent into a ring is arranged within an annular groove formed on a valve housing. The annular groove is limited in the radial direction by a sleeve. Openings, through which the pressurized medium can reach into the interior of the valve housing, are formed both in the sleeve and also in the groove base of the annular groove. In addition, the band is made from spring steel and is pretensioned outwardly in the radial direction.
If the pressure in the interior of the valve housing exceeds the pressure of the pressurized medium arising at the opening of the sleeve, then the band contacts the inner casing surface of the sleeve and thus prevents the pressurized medium flow from the interior of the valve housing to the opening of the sleeve. In the reverse case, the band is forced inward by the pressurized medium arising at the opening of the sleeve, wherein pressurized medium can be guided from the opening of the sleeve into the interior of the valve housing.
This installation-space saving variant of a non-return valve has the disadvantage that the assembly in a surrounding construction is very complicated and subject to errors due to the radially outward directed pretensioning of the band. Because the annular grooves must be sealed relative to the surrounding construction in the mounted state, the outer diameter of the valve housing is adapted to the inner diameter of the surrounding construction and the valve housing is integrated by means of a clearance fit in the surrounding construction. Here, the radially outwardly pretensioned band has the tendency to expand outward, wherein this projects from the annular groove. During assembly, this band could be damaged or could become jammed between the surrounding construction and the valve housing. Therefore, the functional security of the non-return valve or even the entire control valve comes into question.
In an alternative embodiment, the band forming the closing body is arranged within an annular groove, which is formed on the inner casing surface of the valve housing. Here, the band is pretensioned outward in the radial direction. For a flow of pressurized medium into the valve housing, it is bent radially inward, while it otherwise contacts the groove base of the annular groove and thus blocks the outward flow of pressurized medium. In this embodiment, the complicated assembly of the closing body has a disadvantageous effect. Furthermore, there is the risk that the band will move into the region of the control piston arranged displaceably within the valve housing and thus prevents its positioning.